Copper Refining: From Ore to Market (Updated 2024)

The hydrometallurgical copper refining process

In hydrometallurgy, water-based solutions are used to extract copper from oxide ores. The most commonly used method is heap leaching, which involves percolating chemical solutions to leach out metals. Crushed copper ore is “heaped” onto an impermeable leach pad and then sprayed with a sulfuric acid solution in order to dissolve the copper from the ore, forming a copper solution.

This is typically followed by solvent extraction and electrowinning (SX/EW). This is a newer refining technology that became widely adopted in the 1980s, and roughly 20 percent of the world’s copper production is now produced via this process.

Solvent extraction begins with an organic solvent, which separates copper from impurities and unwanted material. Next, sulfuric acid is added to strip the copper from the organic solvent, producing an electrolytic solution.

This solution goes through the electrowinning process, a form of electrolysis in which an electrical current passes through the copper solution. Positively charged copper ions in the solution are then plated onto a cathode. At 99.99 percent pure copper, the copper cathode is now a value-added saleable copper product.

The pyrometallurgical copper refining process

In pyrometallurgy, intense heat, often at 2,300 degrees Fahrenheit, is applied to extract copper from sulfide ores. After the flotation process described above, the next steps are thickening, smelting in a refiner and electrolysis to produce high-purity copper cathodes.

During the thickening stage, the froth solution produced during flotation is poured into large tanks, allowing solids to settle at the bottom. The solution is then then filtered to remove excess water. At the end of this stage, the resulting copper concentrate is ready to be sent to the smelter.

Chemical reactions that occur during the smelting process cause the concentrate to separate into two layers of molten material: a matte layer and a slag layer. The matte layer, on the bottom, contains the copper, while the slag layer contains the impurities.

The slag is discarded and the matte is recovered and moved to a cylindrical vessel called a converter. A variety of chemicals are added to the converter, and these react with the copper to form blister copper, which is usually 98 percent to 99.5 percent pure. The blister copper is then recovered and subjected to a process called fire refining.

In fire refining, air is blown through the copper to oxidize impurities into slag, then wood is added to help reduce the oxidized copper through chemical reactions, leaving refined copper behind to be processed into copper anode.

Finally, to completely deoxidize the copper, either phosphorus is added to it to form phosphorus pentoxide, or the copper is cast into copper anodes and placed in an electrolytic copper cell. Once charged, the pure copper collects on the cathode and is removed as a 99.99 percent pure copper product.

How is refined copper sold?

Refined copper is sold mostly in the form of 99.99 percent purity copper cathode either by smelting companies or mining companies with their own refining plants. The buyers are normally end users such as copper mills, brass mills or foundries who purchase copper cathode as melting stock for the manufacture of copper wire rods, copper ingots or copper alloys.

The price of refined copper is set by the global exchanges, such the London Metal Exchange (LME), the CME Group's COMEX or the Shanghai Futures Exchange (SHFE), and can be brought to market through these exchanges.

Copper cathode sold on the global exchanges must be registered Grade A type with a copper content of 99.99 percent. Unregistered high-grade copper cathode, standard grade and off-grade can be sold into the physical market through trading companies and financial institutions, but will not garner the producer’s premium prices of SHFE or LME registered copper cathode. This premium allows the copper cathode producer to recoup the costs such as insurance and freight associated with transporting its goods to the buyer.